The present invention relates to a method of replicating a microstructure of a metal part. More particularly, the present invention relates to a method of determining a depth of intergranular attack (IGA) on a surface of a metal part, such as those used in an aircraft engine.
Metal parts may be prone to developing cracks, especially when exposed to extreme conditions. For example, a gas turbine engine operates at extreme temperatures and pressures. As a result, parts within the engine, such as blades and vanes, may crack. A repair process for a blade or vane within an assembly includes filling the cracks with liquid metal and then heat treating the blade or vane assembly. Prior to filling the cracks with liquid metal, the blade or vane assembly may commonly be cleaned with an acid such as hydrofluoric acid. The acid may result in a surface attack of the assembly. The surface attack may be so destructive, in some cases, that it is not worthwhile to repair the original crack or cracks in the assembly. As such, it is necessary to determine the extent of the surface attack and the depth of the intergranular attack, before repairing a cracked blade or vane assembly.
A small portion or sample of the assembly may be cut-out and placed under a microscope in order to view the microstructure of the sample and determine a depth of intergranular attack in the assembly. However, this technique requires that the sample be rewelded to the assembly and that the assembly then be heat treated. Alternatively, a replacement portion may be welded into the assembly, but the same steps must be followed in either case. This technique is not only destructive to the assembly, but is also time consuming. There is a need for a non-destructive method of accurately determining the depth of intergranular attack in a metal alloy part.